This invention relates to an electric connection box (i.e., an electric junction block) used as an electric power distribution device (such for example as a relay box, a fuse box, an electronic control unit box, etc.) electrically connected to a battery and various electric loads on a vehicle such as an automobile, and more particularly to an electric connection box which is suitably used for selectively supplying electric power to the electric loads by effecting an on-off control of transistors provided in corresponding relation to the electric loads.
Generally, the supply of electric power to electric loads on a vehicle has heretofore been controlled via electromagnetic relays (i.e., mechanical relays) and fuses. The electromagnetic relays and the fuses are accommodated within a box body of an electric connection box. In the electric connection box to be actually mounted on the vehicle, a plurality of relays, as well as a plurality of fuses, corresponding in number to the electric loads are accommodated within the box body. FIG. 8 is a perspective view showing a conventional electric connection box 300 of the mechanical relay type.
In this electric connection box 300, various connectors 311 are provided at a side face portion of a box body 310, and circuit boards 350 each having electric parts (i.e., relays, etc.) are mounted respectively on upper and lower sides of the box body 310.
In recent years, in order to achieve a compact and lightweight design of an electric connection box and a high-speed switching control, transistors such as power MOSFETs have been increasingly used instead of electromagnetic relays, and electric connection boxes employing transistors have now been described in Patent Literature (see, for example, Patent Literature JP-A-2001-211529).
An electric connection box disclosed in the above Patent Literature 1 includes a bus bar board in which bus bars made of a metal sheet are mounted at least on a surface of an insulating board to thereby form a bus bar circuit, and this bus bar board is accommodated within an insulating case. This electric connection box further includes switch elements each having a plurality of external terminals, and the switch elements are surface mounted on the bus bars of the bus bar board, and are incorporated in the bus bar circuit via the external terminals. Further, a printed circuit is formed integrally on part of the surface of the bus bar board, and at least part of the external terminals of the switch element is connected to this printed circuit. In this case, the switch element has the external terminal on its mounting surface, and this external terminal is directly connected to the bus bar. Also, at least part of the external terminals of the switch element are connected to the bus bar via wires.
When transistors are used instead of electromagnetic relays, a thin design and a compact and lightweight design of an electric connection box can be achieved. However, in the conventional electric connection box of Patent Literature 1, particularly measures to achieve a sufficiently-thin design were not taken, and it was difficult to fully meet the requirement of such a thin design.